For the next 10 to 20 years, a large percentage of “new” building projects will consist of refurbishing and retrofitting existing structures. Whether it’s to save money in tough economic times, increase safety, preserve historic buildings, or achieve green design goals such as LEED certification, many experts would agree that a large percentage of “new” building projects will leverage existing structures.
At the same time, the drive to building information modeling (BIM) and the use of 3D software has penetrated the building industry to such an extent that flat drawings are no longer acceptable for large and even mid-size building projects. However, generating an accurate rendering for structural; mechanical, electrical and plumbing (MEP); and design purposes from CAD, as-builts and site observations are time-consuming and costly.
Using tape measure and notebooks, field personnel can bring back enough data points to construct a model from scratch, however, this process is quite time consuming. Additionally, try as we might, even the best physical measurements will produce inaccuracies, which means model accuracy will suffer as well. As a result, object validation will often require multiple site visits. In addition, most projects begin with two-dimensional measurements, not three-dimensional, further reducing the completeness of any model.
With improvements to high definition scanning (HDS), there is an alternative.
Getting down to reality
Established in civil engineering for the last 10 years, 3D laser scanning is now gaining traction in the AEC community as a faster way to obtain more accurate data points for retrofits. More and more companies are requiring services for building scanning and BIM creation from the point cloud output. In fact, the renowned 80:20 rule also applies to scanning. One year ago, less than 20 percent of scanning service providers were producing BIM models in Revit from point clouds. Today, these same scanning service providers are likely converting more than 80 percent of their building scan requests to BIM.
AEC firms feel the pain of a poor model downstream on the construction side of their business and have been looking to laser scanning to fulfill the promise of more accurate models. Accuracy for as-built models is important because no building in the real world is perfect. Construction for retrofits, in particular, needs as much data as possible regarding imperfections in current conditions. For example, how level is the floor? In what way is it not level and by how much in a given location? Laser scans can help designers understand these realities to ensure that when new fabrications are ready for construction, they work seamlessly with existing components. The more accurate the model, the more precise the construction, and the less time and money is wasted with onsite rework.
Growth of HD laser scanning for building projects
Taking as-built measurements using tape measures and notebooks can result in tolerances from a few inches to two feet or more — depending on the size of a project. By comparison, the tolerances produced when using HD laser scanning are in the millimeter range. The latest in high definition scanners is able to capture 50,000 data points per second — including non-linear objects — and can accumulate billions of points in a few minutes, in addition to color detail and light intensity. Now the data from sites can be extracted in hours versus days — and at much more accurate levels.
To properly capture as-built information, scanner configuration is key. And it is not always simple. Depending on the project, the number of scans and scanner positions required to identify key objects should be planned in advance. For example, to capture data regarding building services the field staff will need several scans from different angles and will likely need to remove ceiling tiles to access pipes, HVAC ducts, and service corridors. An interior scan can take from 15 to 20 minutes, while a wide angle outdoor scan may take between 30 and 40 minutes a scan including set up.
In buildings such as airports, manufacturing sites, and industrial facilities, supporting columns, beams, and trusses often are exposed, and the laser scanner can “see” them and immediately collect their x, y, and z coordinate information into the point cloud. If structural columns and beams are not exposed, field personnel can scan ceiling spaces to obtain supporting column, truss, and cross member information. In some cases, surveyors may not only have to scan; they might also have to perform on-site inspection to identify specific architectural and structural elements using non-destructive methods to locate beams or other hidden structures.
In either case, starting with HD laser scans means these actions are taken more for validation than model creation.
“Scanning can dramatically reduce the amount of time spent in design coordination against existing conditions and really pays [off] during the construction administration phase with reduced requests for information.” says Kelly Cone, associate and innovation director at the Beck Group.
The Beck Group recently produced a BIM model from HD laser scans to support the $9.5 million restoration, rehabilitation, and adaptive reuse of the historic Hinman Research Building at Georgia Tech’s College of Architecture.
The BIM model was used successfully to update and retrofit the original 1939 building by fostering collaboration between the architectural team and the construction manager. The Beck Group created a construction-level model to help realize the design within budget and on schedule. In addition, Beck created intelligent models to support the design, fabrication, and installation of architectural millwork.
“On project completion, we’ll be able to provide Georgia Tech’s facilities management with a complete model, allowing them to monitor and manage building performance over its entire lifecycle,” Cone says.
The long and winding road: Creating a model from a point cloud
At $40,000 each for the least expensive units, laser scanners are a significant investment. If an AEC firm plans to use scanning repeatedly and can develop the in-house expertise, it might make sense to bring scanning in-house. In the meantime, most companies contract with existing partner survey firms to undertake this work.
Either way, after scanning, the design team still just has digital points in a point cloud that do not represent built geometry. Up until recently, the process of identifying geometry in a point cloud to build a model in Revit has been an arduous, time-consuming task that often required too many complicated steps.
Here’s a brief description of this complex software path from a cloud to a model:
From a typical Leica HD scanner, the point cloud needs to be “registered” using Leica Cyclone software. Next, the file could go to Truview or CloudWorx and on to several other geometry recognition software/tools that help identify the points that make up walls, ducts, pipes, and structural members. These tools help users to work the point cloud into AutoCAD, and then port AutoCAD data into Revit to use as a background, from which they would build a model in Revit.
Then, the model from Revit is imported yet again to Navisworks to look at the original point cloud inside the Revit model. Several iterations between Cyclone and CloudWorx — and then more back and forth between Revit and Navisworks — made getting an accurate model in Revit a long, expensive, and resource-intensive process. However, for all the reasons stated in the beginning of this article, firms seeking to exploit the benefits of BIM have persisted along this long and winding road because it was the only way forward.
A welcome shortcut: Direct from scan to model
As the promise of scanning technology and BIM converge, the process of conversion from the cloud to model is still widely recognized as a significant undertaking. Even the Government Services Administration (GSA), with its announcement of more than $180 million in scanning funding, sees the value that the process brings, but is nevertheless still concerned about how many dollars per square foot that accuracy costs to produce. To help, scanner technology has steadily improved and come down in price — so too has the software that processes point clouds to populate modeling applications for design, structural, and MEP work.
“We realized that if modeling software could read a point cloud directly, designers could perform conversions more easily, eliminating much of the workflow complexity by collapsing many steps into one,” says Matt Mason, director of software development at IMAGINiT Technologies.
A software solution that translates point clouds into a standard PTS or PTX file — which Revit can read — was designed and built. By storing the point cloud as a separate database and using a plug-in to Revit that calls only the points necessary for each view, the solution eliminates the tendency for models to bloat in size. The Revit add-on also can recognize geometry and perform tasks such as “building” a wall, starting work from the cloud, or creating a full-blown model directly from laser scans. Similarly, the application can recognize piping and ductwork and build them into the model as well.
Working from reality
“Working from ‘reality’ on the desktop reduces the amount of time required to go back to the field,” says Cone. “On the Georgia Tech project, this meant that we could produce highly accurate fabrication drawings for difficult-to-model objects. We actually fabricated extremely intricate mill work relating to stairs that were close to a hundred years old, in which nothing was plumb or true, based on the models from laser scans.”
The team took the fabrication drawings for staircase millwork right from the model. The final installed work was within millimeters of the aged staircase. This level of accuracy previously was not possible, and Beck avoided what could have been weeks of rework, saving time in the initial installation.
Structural engineers can use the same technique to send fabrication instructions for structural members to manufacturers with the same level of increased accuracy. As laser scanner technology and conversion software improve, the BIM challenge turns to significant opportunity and will foster new techniques and designs for building preservation, energy, and seismic retrofits and architectural renewal projects. The road to BIM just got a whole lot smoother — again.
Laser scanning for construction monitoring and structural deformations
Engineers can also take advantage of HD 3D laser scanning to detect structural deformations that could lead to failure or reduced structure life. In this application, the scan is used to detect tiny deformations that visual and other forms of inspection could not capture.
Beau Turner is director of business development for IMAGINiT Technologies and can be reached at 757-515-3502 or firstname.lastname@example.org.